Rational and Rationale

“Rational” is an adjective meaning “reasonable” or “logical”: “Ivan made a rational decision to sell his old car when he moved to New York.” “Rational” rhymes with “national.”

“Rationale” is a noun which most often means ”underlying reason”: “His rationale for this decision was that it would cost more to pay for parking than the car was worth.” “Rationale” rhymes with “passion pal.”

When you’re explaining the reasoning behind your position, you’re presenting your rationale. But if you’re just making up some lame excuse to make your position appear better—whether to yourself or others—you’re engaging in rationalization.